The art of concealing information has existed for millennia and is one to which computers have been readily adapted. It is known, for example, to use computers for encrypting data using various symmetric and asymmetric cryptographic schemes such as the Data Encryption Standard (DES) and RSA encryption, and cryptographic software packages such as PGP (Pretty Good Privacy). Another technique for concealing information for which computers are used is data hiding or steganography, in which the existence of certain information is concealed within a carrier communication. In contrast to cryptography, where it is a goal to make a message undecipherable regardless of its detection, with steganography it is a goal to hide the very existence of the hidden message. An example of a known steganography technique using computers is to embed a digital watermark into a digital image.
According to the present invention, a method of hiding data is provided. A message to be hidden and an encrypting sequence are provided along with a carrier signal that conveys information (unrelated to the message). An encrypted message is generated based on the message and the encrypting sequence. The encrypted message is embedded into the carrier signal by performing an exclusive-OR of the encrypted message with a first portion of the carrier signal.
In preferred embodiments, the carrier signal is a digital image, and the first portion of-the carrier signal is an LSB plane of the digital image. The digital image has a plurality of color planes, the first portion of the carrier signal is an LSB plane of a first color plane, and the second portion of the carrier signal is an LSB plane of a second color plane.
According to another aspect of the invention, the carrier signal is transmitted to a receiving location. The encrypted message is extracted and from the carrier signal and deciphered at the receiving location. In preferred embodiments, the encrypted sequence is generated based on an encrypting key. The encrypted message is generated by performing an exclusive-OR of the message with the encrypting sequence.
According to yet another aspect of the invention, a method of data hiding is provided in which an encryption key and a carrier signal that conveys information unrelated to the encryption key are supplied. An encryption sequence based on the encryption key is generated. The encryption sequence is embedded into the carrier signal.
In preferred embodiments, the encryption key is a public key for an asymmetric encryption algorithm. The carrier signal can be a signal such as a digital image, digital audio, or digital video. The encryption sequence is substantially random, and can be generated based on a linear feedback shift register. The encryption sequence is embedded into the carrier signal by performing an exclusive-OR of the encryption sequence with a portion of the carrier signal.
According to other aspects of the invention, the carrier signal including the embedded encryption sequence is transmitted to a receiving location. The encryption sequence is extracted from the composite signal at the receiving location. The encryption sequence is decrypted to obtain the encryption key. The encryption key is used to generate an encrypted message at the receiving location, and the encrypted message is transmitted from the receiving location.
According to yet another aspect of the invention, a method of data hiding is provided. An encrypted message is embedded into a first portion of a carrier signal and message extraction information is embedded into a second portion of the carrier signal for extracting the encrypted message from the first portion of the carrier signal.
In preferred embodiments, the encrypted message is embedded by performing an exclusive-OR of the encrypted message with the first portion of the carrier signal. The message extraction information is embedded by performing an exclusive-OR of the first portion of the carrier signal with the second portion of the carrier signal. The first and second portions of the carrier signal can be first and second bit-planes of a digital image.
According to still another aspect of the invention, a method of exchanging data hidden in a carrier signal is provided. A signal including hidden data is generated by transforming a carrier signal from a first domain into a second domain. A message is embedded into the carrier signal in the second domain. The carrier signal is transformed back from the second domain to the first domain. The signal including hidden data is sent to a receiving location. The message is obtained from the signal including hidden data at the receiving location by transforming the signal including hidden data into the second domain and extracting the message.
In preferred embodiments, the message is encrypted prior to generating the signal including hidden data. The message is decrypted after obtaining the message from the signal including hidden data.
According to still yet another aspect of the invention, a data hiding apparatus is provided. An encryption sequence generator generates an encryption sequence based on an encrypting key. An encrypted message generator generates an encrypted message based on the encryption sequence and an input message. An encrypted message embedder embeds the encrypted message into a carrier signal.
In preferred embodiments, the encryption sequence generator generates a substantially random encryption sequence. The encrypted message embedder performs an exclusive-OR of the encrypted message with a portion of the carrier signal. The encrypted message embedder replaces a first LSB plane of a digital image with information based on a second LSB plane of the digital image and performs an exclusive-OR of-the encrypted message with the second LSB plane of the digital image. The encrypted message generator performs an exclusive-OR of the input message with the encrypting sequence to generate the encrypted message.
Additional features of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of the preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.